1. Field of the Invention
The present invention relates generally to a wireless power receiver and a control method thereof, and more particularly, to a wireless power receiver capable of communicating in a predefined way and a control method thereof.
2. Description of the Related Art
A mobile terminal, such as, for example, a cellular phone or a Personal Digital Assistant (PDA), is powered by a rechargeable battery. In order to charge the rechargeable battery, electrical energy is supplied to the battery of the mobile terminal using a separate charging device. Typically, the charging device and the battery are both provided with a separate external contact terminal, so that the charging device and the battery are electrically connected by establishing contact between the external contact terminals.
However, a contact-type charging method is problematic in that the contact terminals can be contaminated with foreign substances because they protrude outward, thereby resulting in improper battery charging. Further, when the contact terminals are exposed to moisture, battery charging is not properly performed.
Wireless charging, or contactless charging technology, has been developed and applied to many electronic products in order to solve the above problems.
Wireless charging technology uses wireless power transmission/reception, examples of which include a system that can automatically charge a battery of a cellular phone by placing the cellular phone on a charging pad, without connecting the cellular phone to a separate charging connector. Electronic products that employ this technology include, for example, a wireless electric toothbrush and a wireless electric shaver, which are generally known to the public. The wireless charging technology is advantageous in that it can improve the waterproof function of an electronic product by wirelessly charging the electronic product. The wireless charging technology is also advantageous in that it can enhance the portability of the electronic product because it is not necessary to use a wired charger.
The wireless charging technology is roughly divided into an electromagnetic inductive coupling method using coils, a magnetic resonance coupling method using resonance, and a Radio Frequency (RF)/microwave radiation method in which electrical energy is transmitted via a microwave into which the electrical energy is converted.
The electromagnetic inductive coupling method has been the mainstream method of wireless charging, but a series of experiments to wirelessly transmit power at distances of several tens of meters by using a microwave have recently achieved success at home and abroad.
The electromagnetic inductive coupling method transfers power between primary and secondary coils. An induced current is produced when a magnet moves relative to a coil of wire. Using this principle, a magnetic field is generated at a transmitting end, and a current is induced at a receiving end, according to a change in the magnetic field in order to produce energy. This effect is referred to as the magnetic induction effect. A power transfer method using the magnetic induction effect is excellent in energy transmission efficiency.
The magnetic resonance coupling method originated with a system that can wirelessly transfer electricity even at several meters distance from a charging device by using the magnetic resonance power transfer principle based on the coupled mode theory. The wireless charging system used the physical concept of resonance, which is the phenomenon in which a wine glass resonates at a same oscillation frequency as an adjacent resonating tuning fork. Instead of sound, an electromagnetic wave carrying electric energy was made to resonate. Since this resonant electromagnetic wave is directly transferred only when a device having the resonance frequency exists, and its unused portion is reabsorbed into the electromagnetic field instead of spreading in the air, it is thought that unlike other electromagnetic waves, the resonant electromagnetic wave will have no influence on surrounding machines or human bodies.
Research on the wireless charging technology has been actively conducted, but a proposal has not been made to establish a standard for wireless charging priority, wireless power transmitter/receiver search, communication frequency selection between a wireless power transmitters and a wireless power receiver, wireless power control, matching circuit selection, communication time distribution for each wireless power receiver in one charging cycle, and the like.